How to waterproof a deck with a shed underneath?

Our 12x12 deck has wooden boards with space in between and years ago we built a shed underneath. The builders put corrugated plastic sheets under the deck so dirt and water would drain out the front of the shed. Well these ended up just holding onto mildew and yuck. Took them down today and am wondering what we can do now to keep water and dirt out of the shed. I was thinking of putting a type of outdoor carpet but have read it will cause the deck to rot. Any ideas? The deck is covered so any water will not dry up as it would with sun on it.

  6 answers
  • Sharon Sharon on Jun 13, 2019

    I think I would get some kind of flexible plastic and make a trough over the shed roof only. Make sure to have one end lower so the water can drain somewhere. Anything else is going to contribute to deck rot if you close it in.

  • Melinda Melinda on Jun 13, 2019

    Maybe you could replace the plastic corrugated sheeting with metal, and create a steeper incline? That plus the occasional oxi-clean based laundry detergent diluted in a bucket of water toseed down there (we had a green mold issue once, that was the easiest treatment).

    • Melinda Melinda on Jun 13, 2019

      There was a need to wipe off the mold, so maybe consider configuring something accessible by a pole extension for cleaning?

  • Kelli L. Milligan Kelli L. Milligan on Jun 13, 2019

    I agree with Sharon. Your best options are to basically roof the shed or pull up your deck boards and do the waterproof flooring system made for that.

  • Emily Emily on Jun 13, 2019

    You don't say how high the shed is but you need a roof on it, and drainage for that roof. And of course it should be lower than the deck. We have a porch over a porch and the upper porch has decking and the lower porch in addition to decking has a ceiling. In between the upper decking and the lower roof is a hip roof that is angled down.

    comment photo
  • William William on Jul 01, 2019

    I would clean up the corrugated plastic and use it for the roof. Just tilt it so it drains down the corrugations to an outside wall. Add a gutter at the low end. Cut a hole in the wall for a downspout elbow to the outside. Add another elbow facing down. Add a downspout. Caulk around the elbow on the inside.

  • Fastlights Fastlights on Jul 12, 2019

    I am suggesting that you use your old car's cover and maybe put that on the top of your roof so that it would be easier to clean. Just pull the cover and remove the dirt at least once a moth.

    I used mine from and made it as a side cover for my shed during rainy season.